Selective etch of silicon by way of metastable hydrogen termination

ABSTRACT

Methods of etching exposed silicon on patterned heterogeneous structures is described and includes a remote plasma etch formed from a fluorine-containing precursor and a hydrogen-containing precursor. Plasma effluents from the remote plasma are flowed into a substrate processing region where the plasma effluents react with the exposed regions of silicon. The plasmas effluents react with the patterned heterogeneous structures to selectively remove silicon while very slowly removing other exposed materials. The silicon selectivity results, in part, from a preponderance of hydrogen-containing precursor in the remote plasma which hydrogen terminates surfaces on the patterned heterogeneous structures. A much lower flow of the fluorine-containing precursor progressively substitutes fluorine for hydrogen on the hydrogen-terminated silicon thereby selectively removing silicon from exposed regions of silicon. The silicon selectivity also results from the presence of an ion suppressor positioned between the remote plasma and the substrate processing region. The ion suppressor reduces or substantially eliminates the number of ionically-charged species that reach the substrate. The methods may be used to selectively remove silicon far faster than silicon oxide, silicon nitride and a variety of metal-containing materials.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of and claims benefit to U.S. patentapplication Ser. No. 13/439,079 filed on Apr. 4, 2012, which claims thebenefit of U.S. Prov. Pat. App. No. 61/544,747 filed Oct. 7, 2011, andtitled “SELECTIVE ETCH OF SILICON BY WAY OF METASTABLE HYDROGENTERMINATION,” both of which are incorporated herein by reference for allpurposes.

BACKGROUND OF THE INVENTION

Integrated circuits are made possible by processes which produceintricately patterned material layers on substrate surfaces. Producingpatterned material on a substrate requires controlled methods forremoval of exposed material. Chemical etching is used for a variety ofpurposes including transferring a pattern in photoresist into underlyinglayers, thinning layers or thinning lateral dimensions of featuresalready present on the surface. Often it is desirable to have an etchprocess which etches one material faster than another helping e.g. apattern transfer process proceed. Such an etch process is said to beselective to the first material. As a result of the diversity ofmaterials, circuits and processes, etch processes have been developedwith a selectivity towards a variety of materials. However, there arefew options for selectively etching silicon nitride faster than silicon.

Dry etch processes are often desirable for selectively removing materialfrom semiconductor substrates. The desirability stems from the abilityto gently remove material from miniature structures with minimalphysical disturbance. Dry etch processes also allow the etch rate to beabruptly stopped by removing the gas phase reagents. Some dry-etchprocesses involve the exposure of a substrate to remote plasmaby-products formed from one or more precursors. For example, remoteplasma generation of nitrogen trifluoride in combination with ionsuppression techniques enables silicon to be selectively removed from apatterned substrate when the plasma effluents are flowed into thesubstrate processing region. However, the silicon selectivityoccasionally needs to be even higher for certain applications, forexample, the removal of “dummy” gates of polysilicon before a workinggate can be formed.

Methods are needed to increase silicon selectively relatively to siliconoxide, silicon nitride and other materials for dry etch processes.

BRIEF SUMMARY OF THE INVENTION

Methods of etching exposed silicon on patterned heterogeneous structuresis described and includes a remote plasma etch formed from afluorine-containing precursor and a hydrogen-containing precursor.Plasma effluents from the remote plasma are flowed into a substrateprocessing region where the plasma effluents react with the exposedregions of silicon. The plasmas effluents react with the patternedheterogeneous structures to selectively remove silicon while very slowlyremoving other exposed materials. The silicon selectivity results, inpart, from a preponderance of hydrogen-containing precursor in theremote plasma which hydrogen terminates surfaces on the patternedheterogeneous structures. A much lower flow of the fluorine-containingprecursor progressively substitutes fluorine for hydrogen on thehydrogen-terminated silicon thereby selectively removing silicon fromexposed regions of silicon. The silicon selectivity also results fromthe presence of an ion suppressor positioned between the remote plasmaand the substrate processing region. The ion suppressor reduces orsubstantially eliminates the number of ionically-charged species thatreach the substrate. The methods may be used to selectively removesilicon far faster than silicon oxide, silicon nitride and a variety ofmetal-containing materials.

Embodiments of the invention include methods of etching a patternedsubstrate in a substrate processing region of a substrate processingchamber. The patterned substrate has exposed silicon. The method includeflowing each of a fluorine-containing precursor and ahydrogen-containing precursor into a remote plasma region fluidlycoupled to the substrate processing region while forming a remote plasmain the remote plasma region to produce plasma effluents. The atomic flowratio of the precursors is greater than or about 25:1 H:F and formingthe remote plasma in the remote plasma region to produce the plasmaeffluents comprises applying RF power between about 10 Watts and about2000 Watts to the plasma region. The methods further include etching theexposed silicon by flowing the plasma effluents into the substrateprocessing region through through-holes in a showerhead. The temperatureof the patterned substrate during the etching operation is greater thanor about 0° C. and the pressure within the substrate processing regionis above or about 0.05 Torr and below or about 10 Torr.

Additional embodiments and features are set forth in part in thedescription that follows, and in part will become apparent to thoseskilled in the art upon examination of the specification or may belearned by the practice of the disclosed embodiments. The features andadvantages of the disclosed embodiments may be realized and attained bymeans of the instrumentalities, combinations, and methods described inthe specification.

BRIEF DESCRIPTION OF THE DRAWINGS

A further understanding of the nature and advantages of the disclosedembodiments may be realized by reference to the remaining portions ofthe specification and the drawings.

FIG. 1 is a flow chart of a silicon selective etch process according todisclosed embodiments.

FIG. 2A shows a substrate processing chamber according to embodiments ofthe invention.

FIG. 2B shows a showerhead of a substrate processing chamber accordingto embodiments of the invention.

FIG. 3 shows a substrate processing system according to embodiments ofthe invention.

In the appended figures, similar components and/or features may have thesame reference label. Further, various components of the same type maybe distinguished by following the reference label by a dash and a secondlabel that distinguishes among the similar components. If only the firstreference label is used in the specification, the description isapplicable to any one of the similar components having the same firstreference label irrespective of the second reference label.

DETAILED DESCRIPTION OF THE INVENTION

Methods of etching exposed silicon on patterned heterogeneous structuresis described and includes a remote plasma etch formed from afluorine-containing precursor and a hydrogen-containing precursor.Plasma effluents from the remote plasma are flowed into a substrateprocessing region where the plasma effluents react with the exposedregions of silicon. The plasmas effluents react with the patternedheterogeneous structures to selectively remove silicon while very slowlyremoving other exposed materials. The silicon selectivity results, inpart, from a preponderance of hydrogen-containing precursor in theremote plasma which hydrogen terminates surfaces on the patternedheterogeneous structures. A much lower flow of the fluorine-containingprecursor progressively substitutes fluorine for hydrogen on thehydrogen-terminated silicon thereby selectively removing silicon fromexposed regions of silicon. The silicon selectivity also results fromthe presence of an ion suppressor positioned between the remote plasmaand the substrate processing region. The ion suppressor reduces orsubstantially eliminates the number of ionically-charged species thatreach the substrate. The methods may be used to selectively removesilicon far faster than silicon oxide, silicon nitride and a variety ofmetal-containing materials.

Siconi™ etch processes have used a hydrogen source such as ammonia (NH₃)and a fluorine source such as nitrogen trifluoride (NF₃) which togetherflow through a remote plasma system (RPS) and into a reaction region.The flow rates of ammonia and nitrogen trifluoride are typically chosensuch that the atomic flow rate of hydrogen is roughly twice that offluorine in order to efficiently utilize the constituents of the twoprocess gases. The presence of hydrogen and fluorine allows theformation of solid byproducts of (NH₄)₂SiF₆ at relatively low substratetemperatures. The solid byproducts are removed by raising thetemperature of the substrate above the sublimation temperature. Siconi™etch processes remove silicon oxide more rapidly than silicon. Theinventors have discovered that the selectivity can be inverted byincreasing the atomic flow ratio of hydrogen:fluorine. Without bindingthe coverage of the claims to hypothetical mechanisms which may or maynot be entirely correct, the inventors hypothesize that thepreponderance of hydrogen radicals maintains a stable hydrogentermination on a broad array of exposed materials. The exposure tohydrogen radicals also hydrogen terminates silicon surfaces, however,the lower density fluorine radicals break the Si—H bonds to form Si—Fbonds until volatile SiF_(x) species desorb from the surface and areevacuated from the substrate processing region. The open bonding sitesleft behind by the desorption are quickly hydrogen terminated and theprocess continues.

In order to better understand and appreciate the invention, reference isnow made to FIG. 1 which is a flow chart of a silicon selective etchprocess according to disclosed embodiments. Silicon may be amorphous,crystalline or polycrystalline (in which case it is usually referred toas polysilicon). Prior to the first operation, a structure is formed ina patterned substrate. The structure possesses separate exposed regionsof silicon and silicon oxide. The substrate is then delivered into aprocessing region (operation 110).

Hydrogen (H₂) is flowed into a plasma region separate from the substrateprocessing region (operation 120). The separate plasma region may bereferred to as a remote plasma region herein and may be within adistinct module from the processing chamber or a compartment within theprocessing chamber. Generally speaking, an hydrogen-containing precursormay be flowed into the plasma region and the oxygen-containing precursormay comprise at least one precursor selected from H₂, NH₃, hydrocarbons,or the like. A flow of nitrogen trifluoride is also introduced into theremote plasma region (operation 125) where it is simultaneously excitedin a plasma along with the hydrogen. The flow rate of the nitrogentrifluoride is low relative to the flow rate of the hydrogen to effect ahigh atomic flow ratio H:F as will be quantified shortly. Other sourcesof fluorine may be used to augment or replace the nitrogen trifluoride.In general, a fluorine-containing precursor may be flowed into theremote plasma region and the fluorine-containing precursor comprises atleast one precursor selected from the group consisting of atomicfluorine, diatomic fluorine, bromine trifluoride, chlorine trifluoride,nitrogen trifluoride, hydrogen fluoride, fluorinated hydrocarbons,sulfur hexafluoride and xenon difluoride.

The plasma effluents formed in the remote plasma region are then flowedinto the substrate processing region (operation 130). The patternedsubstrate is selectively etched (operation 135) such that the exposedsilicon is removed at a rate at least or about seventy times greaterthan the exposed silicon oxide. The invention involves maintenance of ahigh atomic flow ratio of hydrogen (H) to fluorine (F) in order achievehigh etch selectivity of silicon. Some precursors may contain bothfluorine and hydrogen, in which case the atomic flow rate of allcontributions are included when calculating the atomic flow ratiodescribed herein. The preponderance of hydrogen helps to hydrogenterminate exposed surfaces on the patterned substrate. Under theconditions described herein, hydrogen termination is metastable on onlythe silicon surfaces. Fluorine from the nitrogen trifluoride or otherfluorine-containing precursor displaces the hydrogen on the siliconsurface and creates volatile residue which leaves the surface andcarries silicon away. Due to the strong bond energies present in theother exposed materials, the fluorine is unable to displace the hydrogenof the other hydrogen terminated surfaces (and/or is unable to createvolatile residue to remove the other exposed material). In oneembodiment, a gas flow ratio (H₂:NF₃) greater than or about 15:1, or ingeneral terms, greater than or about an atomic flow ratio of between10:1, was found to achieve etch selectivity (silicon:silicon oxide orsilicon:silicon nitride) of greater than or about 70:1. The etchselectivity (silicon:silicon oxide or silicon:silicon nitride) may alsobe greater than or about 100:1, greater than or about 150:1, greaterthan or about 200:1, greater than or about 250:1 or greater than orabout 300:1 in disclosed embodiments. Regions of exposed tungsten ortitanium nitride may also be present on the patterned substrate and maybe referred to as exposed metallic regions. The etch selectivity(silicon:exposed metallic region) may be greater than or about 100:1,greater than or about 150:1, greater than or about 200:1, greater thanor about 250:1, greater than or about 500:1, greater than or about1000:1, greater than or about 2000:1 or greater than or about 3000:1 indisclosed embodiments. The reactive chemical species are removed fromthe substrate processing region and then the substrate is removed fromthe processing region (operation 145).

The presence of the high flow of hydrogen-containing precursor, asdescribed herein, ensures that silicon, silicon oxide and siliconnitride maintain a hydrogen-terminated surface during much of theprocessing. The fluorine-containing precursor and/or thehydrogen-containing precursor may further include one or more relativelyinert gases such as He, N₂, Ar, or the like. The inert gas can be usedto improve plasma stability and/or to carry liquid precursors to theremote plasma region. Flow rates and ratios of the different gases maybe used to control etch rates and etch selectivity. In an embodiment,the fluorine-containing gas includes NF₃ at a flow rate of between about1 sccm (standard cubic centimeters per minute) and 30 sccm, H₂ at a flowrate of between about 500 sccm and 5,000 sccm, He at a flow rate ofbetween about 0 sccm and 3000 sccm, and Ar at a flow rate of betweenabout 0 sccm and 3000 sccm. One of ordinary skill in the art wouldrecognize that other gases and/or flows may be used depending on anumber of factors including processing chamber configuration, substratesize, geometry and layout of features being etched, and the like. Theflow rate of the fluorine-containing gas may be less than or about 30sccm, less than or about 20 sccm, less than or about 15 sccm or lessthan or about 10 sccm in disclosed embodiments. Lower flow rates of thefluorine-containing gas will generally increase the silicon selectivity.The flow rate of the hydrogen-containing gas may be greater than orabout 300 sccm, greater than or about 500 sccm, greater than or about1000 sccm or greater than or about 2000 sccm in disclosed embodiments.Increasing the flow rate of the hydrogen-containing gas generallyincreases silicon selectivity. The atomic flow ratio H:F should be kepthigh to reduce or eliminate solid residue formation on silicon oxide.The formation of solid residue consumes some silicon oxide which reducesthe silicon selectivity of the etch process. The atomic flow ratio H:Fis greater than or about twenty five (i.e. 25:1), greater than or about30:1 or greater than or about 40:1 in embodiments of the invention.

The method also includes applying energy to the fluorine-containingprecursor and the hydrogen-containing precursor while they are in theremote plasma region to generate the plasma effluents. As would beappreciated by one of ordinary skill in the art, the plasma may includea number of charged and neutral species including radicals and ions. Theplasma may be generated using known techniques (e.g., RF, capacitivelycoupled, inductively coupled, and the like). In an embodiment, theplasma power is applied using a capacitively-coupled plasma unit at asource power of between about 10 W and 2000 W and a pressure of betweenabout 0.2 Torr and 5 Torr. The capacitively-coupled plasma unit may bedisposed remote from a gas reaction region of the processing chamber.For example, the capacitively-coupled plasma unit and the plasmageneration region may be separated from the gas reaction region by anion suppressor.

An ion suppressor may be used to filter ions from the plasma effluentsduring transit from the remote plasma region to the substrate processingregion in embodiments of the invention. The ion suppressor functions toreduce or eliminate ionically charged species traveling from the plasmageneration region to the substrate. Uncharged neutral and radicalspecies may pass through the openings in the ion suppressor to react atthe substrate. It should be noted that complete elimination of ionicallycharged species in the reaction region surrounding the substrate is notalways the desired goal. In many instances, ionic species are requiredto reach the substrate in order to perform the etch and/or depositionprocess. In these instances, the ion suppressor helps control theconcentration of ionic species in the reaction region at a level thatassists the process.

In accordance with some embodiments of the invention, an ion suppressoras described in the exemplary equipment section may be used to provideradical and/or neutral species for selectively etching substrates. Inone embodiment, for example, an ion suppressor is used to providefluorine and hydrogen containing plasma effluents to selectively etchsilicon. Using the plasma effluents, an etch rate selectivity ofsilicon:silicon oxide (or silicon nitride) over seventy may be achieved.The ion suppressor may be used to provide a reactive gas having a higherconcentration of radicals than ions. Because most of the chargedparticles of a plasma are filtered or removed by the ion suppressor, thesubstrate is not necessarily biased during the etch process. Such aprocess using radicals and other neutral species can reduce plasmadamage compared to conventional plasma etch processes that includesputtering and bombardment. Embodiments of the present invention arealso advantageous over conventional wet etch processes where surfacetension of liquids can cause bending and peeling of small features.

Blanket wafers of silicon oxide, silicon and silicon nitride were usedto quantify the etch rates for an exemplary process. A remote plasma wasformed from nitrogen trifluoride, hydrogen (H₂), helium and argon andthe effluents etched blanket wafers of each of the three films inseparate processes. The etch process removed silicon at about twohundred times the rate of silicon oxide and over two hundred times therate of silicon nitride for etch rates of about 400 Å/min. In separateexperiments, the etch process removed silicon at about five hundredtimes the rate of silicon oxide and over five hundred times the rate ofsilicon nitride for etch rates of about 200 Å/min. The etch rate ofsilicon oxide may be greater than or about 100 Å/min, greater than orabout 200 Å/min or greater than or about 300 Å/min in disclosedembodiments. The selectivity, the non-local plasma, the controlled ionicconcentration and the lack of solid byproducts, each make these etchprocesses well suited for delicately removing or trimming siliconstructures removing little or no silicon oxide and little or no siliconnitride.

The temperature of the substrate is greater than 0° C. during the etchprocess. The substrate temperature may be greater than or about 20° C.and less than or about 300° C. At the high end of this substratetemperature range, the silicon etch rate drops. At the lower end of thissubstrate temperature range, silicon oxide and silicon nitride begin toetch and so the selectivity drops. In disclosed embodiments, thetemperature of the substrate during the etches described herein may begreater than or about 30° C. while less than or about 200° C. or greaterthan or about 40° C. while less than or about 150° C. The substratetemperature may be below 100° C., below or about 80° C., below or about65° C. or below or about 50° C. in disclosed embodiments.

The data further show an increase in silicon etch rate as a function ofprocess pressure (for a given hydrogen:fluorine atomic ratio). However,for an atomic flow rate ratio of about 50:1 H:F increasing the pressureabove 1 Torr begins to reduce the selectivity. This is suspected toresult from a higher probability of combining two or morefluorine-containing effluents. The etch process then begins to removesilicon oxide, silicon nitride and other materials. The pressure withinthe substrate processing region may be below or about 10 Torr, below orabout 5 Torr, below or about 3 Torr, below or about 2 Torr, below orabout 1 Torr or below or about 750 mTorr in disclosed embodiments. Inorder to ensure adequate etch rate, the pressure may be above or about0.05 Torr, above or about 0.1 Torr, above or about 0.2 Torr or above orabout 0.4 Torr in embodiments of the invention. Any of the upper limitson pressure may be combined with lower limits to form additionalembodiments. Plasma power applied to the remote plasma region can be avariety of frequencies or a combination of multiple frequencies. The RFpower may be between about 10 Watts and about 2000 Watts, between about200 Watts and about 1800 Watts or between about 750 Watts and about 1500Watts in different embodiments. The RF frequency applied in theexemplary processing system may be low RF frequencies less than about500 kHz, high RF frequencies between about 10 MHz and about 15 MHz ormicrowave frequencies greater than or about 1 GHz in differentembodiments.

A pre-treatment may be used, in embodiments, to remove a thin oxidelayer on the surfaces of the exposed silicon regions. The pre-treatmentoccurs before the operation of etching the exposed silicon. Thin oxidelayers often form when exposing silicon to atmospheric conditions. Thethin oxide layer can make the silicon regions behave more like siliconoxide regions, in part, because the selectivities of the processesreported herein are so high. The thin silicon oxide layer is oftenreferred to as a “native” oxide and may be removed using a variety ofprocesses known to those of skill in the art. For example, a Siconi™etch may be used to remove the native oxide. In other words, afluorine-containing precursor and a hydrogen-containing precursor may becombined in a remote plasma region and excited in a plasma. The atomicflow ratio H:F during the pre-treatment Siconi™ may be between about0.5:1 and about 8:1 to ensure the production of solid by-products on theexposed silicon surfaces. The native oxide is consumed during theproduction of these solid by-products in embodiments of the invention.The temperature of the patterned substrate during the Siconi™ etch maybe below the sublimation temperature of the solid by-products. Thetemperature of the patterned substrate may be raised above thesublimation temperature after formation of the solid by-products toremove the solid by-products. The sublimation completes the removal ofthe native oxide from the exposed silicon.

Alternatively, the native oxide can be removed by a hydrogen plasmaformed in the substrate processing region. The local pre-treatmentplasma is created by applying a local plasma power above or about 200Watts and below or about 3000 Watts or above or about 300 Watts andbelow or about 2000 Watts in embodiments. Regardless of the method used,the native oxide (if present) is removed before the operation of etchingthe exposed silicon. Techniques for removing the native oxide may becarried out in the same substrate processing region used to selectivelyetch the silicon, or each of these processes may be performed inseparate chambers. However, the patterned substrate should not beexposed to moisture or an atmospheric environment during the transferbetween separate chambers. It should also be noted that the terms“exposed silicon region” and “exposed silicon” will be used hereinregardless of whether a native oxide is present.

A post-treatment may be used, in embodiments, to avoid forming residueafter the substrate has been etched and exposed to atmosphericconditions. Residual fluorine on the surface of the patterned substrateis hypothesized to react with moisture from the atmosphere to form smallamounts of hydrofluoric acid (HF). This may cause residues of silicon,titanium or other compounds to form on the surface. The post-treatmentoccurs after the operation of etching the exposed silicon. One treatmentwhich is thought to remove the residual fluorine includes flowing atleast one of N₂, Ar, He, NO₂, N₂O, H₂, NH₃, O₂ or CH₄ into the substrateprocessing region while forming a local plasma by applying a localplasma power above or about 100 Watts and below or about 2000 Watts or3000 Watts. At least one of N₂, Ar, He, NO₂, N₂O, H₂, NH₃, O₂ or CH₄ mayalternatively flow through a remote plasma region with plasma power(between 100 Watts and 2000 Watts or 3000 Watts) applied. The plasmaeffluents may then be flowed into the substrate processing region toremove residual fluorine from the exposed silicon regions of thepatterned substrate. One additional post-treatment involves simplyheating the substrate to between 200° C. and about 600° C. or betweenabout 300° C. and about 600° C. to desorb the residual fluorine inembodiments of the invention. Any of these post-treatments may be usedalone or in combination with any or all of the others to remove residualfluorine from the exposed silicon regions.

Additional process parameters are disclosed in the course of describingan exemplary processing chamber and system.

Exemplary Processing System

Processing chambers that may implement embodiments of the presentinvention may be included within processing platforms such as theCENTURA® and PRODUCER® systems, available from Applied Materials, Inc.of Santa Clara, Calif. Examples of substrate processing chambers thatcan be used with exemplary methods of the invention may include thoseshown and described in co-assigned U.S. Provisional Patent App. No.60/803,499 to Lubomirsky et al, filed May 30, 2006, and titled “PROCESSCHAMBER FOR DIELECTRIC GAPFILL,” the entire contents of which is hereinincorporated by reference for all purposes. Additional exemplary systemsmay include those shown and described in U.S. Pat. Nos. 6,387,207 and6,830,624, which are also incorporated herein by reference for allpurposes.

FIG. 2A is a substrate processing chamber 200 according to disclosedembodiments. A remote plasma system 210 may process thefluorine-containing precursor which then travels through a gas inletassembly 211. Two distinct gas supply channels are visible within thegas inlet assembly 211. A first channel 212 carries a gas that passesthrough the remote plasma system 210 (RPS), while a second channel 213bypasses the remote plasma system 210. Either channel may be used forthe fluorine-containing precursor, in embodiments. On the other hand,the first channel 212 may be used for the process gas and the secondchannel 213 may be used for a treatment gas. The lid (or conductive topportion) 221 and a perforated partition 253 are shown with an insulatingring 224 in between, which allows an AC potential to be applied to thelid 221 relative to perforated partition 253. The AC potential strikes aplasma in chamber plasma region 220. The process gas may travel throughfirst channel 212 into chamber plasma region 220 and may be excited by aplasma in chamber plasma region 220 alone or in combination with remoteplasma system 210. If the process gas (the fluorine-containingprecursor) flows through second channel 213, then only the chamberplasma region 220 is used for excitation. The combination of chamberplasma region 220 and/or remote plasma system 210 may be referred to asa remote plasma system herein. The perforated partition (also referredto as a showerhead) 253 separates chamber plasma region 220 from asubstrate processing region 270 beneath showerhead 253. Showerhead 253allows a plasma present in chamber plasma region 220 to avoid directlyexciting gases in substrate processing region 270, while still allowingexcited species to travel from chamber plasma region 220 into substrateprocessing region 270.

Showerhead 253 is positioned between chamber plasma region 220 andsubstrate processing region 270 and allows plasma effluents (excitedderivatives of precursors or other gases) created within remote plasmasystem 210 and/or chamber plasma region 220 to pass through a pluralityof through-holes 256 that traverse the thickness of the plate. Theshowerhead 253 also has one or more hollow volumes 251 which can befilled with a precursor in the form of a vapor or gas (such as asilicon-containing precursor) and pass through small holes 255 intosubstrate processing region 270 but not directly into chamber plasmaregion 220. Showerhead 253 is thicker than the length of the smallestdiameter 250 of the through-holes 256 in this disclosed embodiment. Inorder to maintain a significant concentration of excited speciespenetrating from chamber plasma region 220 to substrate processingregion 270, the length 226 of the smallest diameter 250 of thethrough-holes may be restricted by forming larger diameter portions ofthrough-holes 256 part way through the showerhead 253. The length of thesmallest diameter 250 of the through-holes 256 may be the same order ofmagnitude as the smallest diameter of the through-holes 256 or less indisclosed embodiments.

Showerhead 253 may be configured to serve the purpose of an ionsuppressor as shown in FIG. 2A. Alternatively, a separate processingchamber element may be included (not shown) which suppresses the ionconcentration traveling into substrate processing region 270. Lid 221and showerhead 253 may function as a first electrode and secondelectrode, respectively, so that lid 221 and showerhead 253 may receivedifferent electric voltages. In these configurations, electrical power(e.g., RF power) may be applied to lid 221, showerhead 253, or both. Forexample, electrical power may be applied to lid 221 while showerhead 253(serving as ion suppressor) is grounded. The substrate processing systemmay include a RF generator that provides electrical power to the lidand/or showerhead 253. The voltage applied to lid 221 may facilitate auniform distribution of plasma (i.e., reduce localized plasma) withinchamber plasma region 220. To enable the formation of a plasma inchamber plasma region 220, insulating ring 224 may electrically insulatelid 221 from showerhead 253. Insulating ring 224 may be made from aceramic and may have a high breakdown voltage to avoid sparking Portionsof substrate processing chamber 200 near the capacitively-coupled plasmacomponents just described may further include a cooling unit (not shown)that includes one or more cooling fluid channels to cool surfacesexposed to the plasma with a circulating coolant (e.g., water).

In the embodiment shown, showerhead 253 may distribute (viathrough-holes 256) process gases which contain oxygen, fluorine and/ornitrogen and/or plasma effluents of such process gases upon excitationby a plasma in chamber plasma region 220. In embodiments, the processgas introduced into the remote plasma system 210 and/or chamber plasmaregion 220 may contain fluorine (e.g. F₂, NF₃ or XeF₂). The process gasmay also include a carrier gas such as helium, argon, nitrogen (N₂),etc. Plasma effluents may include ionized or neutral derivatives of theprocess gas and may also be referred to herein as radical-fluorinereferring to the atomic constituent of the process gas introduced.

Through-holes 256 are configured to suppress the migration ofionically-charged species out of the chamber plasma region 220 whileallowing uncharged neutral or radical species to pass through showerhead253 into substrate processing region 270. These uncharged species mayinclude highly reactive species that are transported with less-reactivecarrier gas by through-holes 256. As noted above, the migration of ionicspecies by through-holes 256 may be reduced, and in some instancescompletely suppressed. Controlling the amount of ionic species passingthrough showerhead 253 provides increased control over the gas mixturebrought into contact with the underlying wafer substrate, which in turnincreases control of the deposition and/or etch characteristics of thegas mixture. For example, adjustments in the ion concentration of thegas mixture can significantly alter its etch selectivity (e.g., siliconnitride:silicon etch ratios).

In embodiments, the number of through-holes 256 may be between about 60and about 2000. Through-holes 256 may have a variety of shapes but aremost easily made round. The smallest diameter 250 of through-holes 256may be between about 0.5 mm and about 20 mm or between about 1 mm andabout 6 mm in disclosed embodiments. There is also latitude in choosingthe cross-sectional shape of through-holes, which may be made conical,cylindrical or combinations of the two shapes. The number of small holes255 used to introduce unexcited precursors into substrate processingregion 270 may be between about 100 and about 5000 or between about 500and about 2000 in different embodiments. The diameter of the small holes255 may be between about 0.1 mm and about 2 mm.

Through-holes 256 may be configured to control the passage of theplasma-activated gas (i.e., the ionic, radical, and/or neutral species)through showerhead 253. For example, the aspect ratio of the holes(i.e., the hole diameter to length) and/or the geometry of the holes maybe controlled so that the flow of ionically-charged species in theactivated gas passing through showerhead 253 is reduced. Through-holes256 in showerhead 253 may include a tapered portion that faces chamberplasma region 220, and a cylindrical portion that faces substrateprocessing region 270. The cylindrical portion may be proportioned anddimensioned to control the flow of ionic species passing into substrateprocessing region 270. An adjustable electrical bias may also be appliedto showerhead 253 as an additional means to control the flow of ionicspecies through showerhead 253.

Alternatively, through-holes 256 may have a smaller inner diameter (ID)toward the top surface of showerhead 253 and a larger ID toward thebottom surface. In addition, the bottom edge of through-holes 256 may bechamfered to help evenly distribute the plasma effluents in substrateprocessing region 270 as the plasma effluents exit the showerhead andthereby promote even distribution of the plasma effluents and precursorgases. The smaller ID may be placed at a variety of locations alongthrough-holes 256 and still allow showerhead 253 to reduce the iondensity within substrate processing region 270. The reduction in iondensity results from an increase in the number of collisions with wallsprior to entry into substrate processing region 270. Each collisionincreases the probability that an ion is neutralized by the acquisitionor loss of an electron from the wall. Generally speaking, the smaller IDof through-holes 256 may be between about 0.2 mm and about 20 mm. Inother embodiments, the smaller ID may be between about 1 mm and 6 mm orbetween about 0.2 mm and about 5 mm. Further, aspect ratios of thethrough-holes 256 (i.e., the smaller ID to hole length) may beapproximately 1 to 20. The smaller ID of the through-holes may be theminimum ID found along the length of the through-holes. The crosssectional shape of through-holes 256 may be generally cylindrical,conical, or any combination thereof.

FIG. 2B is a bottom view of a showerhead 253 for use with a processingchamber according to disclosed embodiments. Showerhead 253 correspondswith the showerhead shown in FIG. 2A. Through-holes 256 are depictedwith a larger inner-diameter (ID) on the bottom of showerhead 253 and asmaller ID at the top. Small holes 255 are distributed substantiallyevenly over the surface of the showerhead, even amongst thethrough-holes 256 which helps to provide more even mixing than otherembodiments described herein.

An exemplary patterned substrate may be supported by a pedestal (notshown) within substrate processing region 270 when fluorine-containingplasma effluents and hydrogen-containing plasma effluents arrive throughthrough-holes 256 in showerhead 253. Though substrate processing region270 may be equipped to support a plasma for other processes such ascuring, no plasma is present during the etching of patterned substrate,in embodiments of the invention.

A plasma may be ignited either in chamber plasma region 220 aboveshowerhead 253 or substrate processing region 270 below showerhead 253.A plasma is present in chamber plasma region 220 to produce theradical-fluorine from an inflow of the fluorine-containing precursor. AnAC voltage typically in the radio frequency (RF) range is appliedbetween the conductive top portion (lid 221) of the processing chamberand showerhead 253 to ignite a plasma in chamber plasma region 220during deposition. An RF power supply generates a high RF frequency of13.56 MHz but may also generate other frequencies alone or incombination with the 13.56 MHz frequency.

The top plasma may be left at low or no power when the bottom plasma inthe substrate processing region 270 is turned on to either cure a filmor clean the interior surfaces bordering substrate processing region270. A plasma in substrate processing region 270 is ignited by applyingan AC voltage between showerhead 253 and the pedestal or bottom of thechamber. A cleaning gas may be introduced into substrate processingregion 270 while the plasma is present.

The pedestal may have a heat exchange channel through which a heatexchange fluid flows to control the temperature of the substrate. Thisconfiguration allows the substrate temperature to be cooled or heated tomaintain relatively low temperatures (from room temperature throughabout 120° C.). The heat exchange fluid may comprise ethylene glycol andwater. The wafer support platter of the pedestal (preferably aluminum,ceramic, or a combination thereof) may also be resistively heated inorder to achieve relatively high temperatures (from about 120° C.through about 1100° C.) using an embedded single-loop embedded heaterelement configured to make two full turns in the form of parallelconcentric circles. An outer portion of the heater element may runadjacent to a perimeter of the support platter, while an inner portionruns on the path of a concentric circle having a smaller radius. Thewiring to the heater element passes through the stem of the pedestal.

The chamber plasma region or a region in a remote plasma system may bereferred to as a remote plasma region. In embodiments, the radicalprecursors (e.g. radical-fluorine and radical-hydrogen) are formed inthe remote plasma region and travel into the substrate processing regionwhere the combination preferentially etches silicon. Plasma power mayessentially be applied only to the remote plasma region, in embodiments,to ensure that the radical-fluorine and the radical-hydrogen (whichtogether may be referred to as plasma effluents) are not further excitedin the substrate processing region.

In embodiments employing a chamber plasma region, the excited plasmaeffluents are generated in a section of the substrate processing regionpartitioned from a deposition region. The deposition region, also knownherein as the substrate processing region, is where the plasma effluentsmix and react to etch the patterned substrate (e.g., a semiconductorwafer). The excited plasma effluents may also be accompanied by inertgases (in the exemplary case, argon). The substrate processing regionmay be described herein as “plasma-free” during the etch of thepatterned substrate. “Plasma-free” does not necessarily mean the regionis devoid of plasma. A relatively low concentration of ionized speciesand free electrons created within the plasma region do travel throughpores (apertures) in the partition (showerhead/ion suppressor) due tothe shapes and sizes of through-holes 256. In some embodiments, there isessentially no concentration of ionized species and free electronswithin the substrate processing region. The borders of the plasma in thechamber plasma region are hard to define and may encroach upon thesubstrate processing region through the apertures in the showerhead. Inthe case of an inductively-coupled plasma, a small amount of ionizationmay be effected within the substrate processing region directly.Furthermore, a low intensity plasma may be created in the substrateprocessing region without eliminating desirable features of the formingfilm. All causes for a plasma having much lower intensity ion densitythan the chamber plasma region (or a remote plasma region, for thatmatter) during the creation of the excited plasma effluents do notdeviate from the scope of “plasma-free” as used herein.

Combined flow rates of fluorine-containing precursor andhydrogen-containing precursor into the chamber may account for 0.05% toabout 20% by volume of the overall gas mixture; the remainder beingcarrier gases. The fluorine-containing precursor and thehydrogen-containing precursor are flowed into the remote plasma regionbut the plasma effluents have the same volumetric flow ratio, inembodiments. In the case of the fluorine-containing precursor, a purgeor carrier gas may be first initiated into the remote plasma regionbefore those of the fluorine-containing gas to stabilize the pressurewithin the remote plasma region.

Plasma power applied to the remote plasma region can be a variety offrequencies or a combination of multiple frequencies. In the exemplaryprocessing system the plasma is provided by RF power delivered betweenlid 221 and showerhead 253. The RF power may be between about 10 Wattsand about 15,000 Watts, between about 10 Watts and about 5000 Watts,between about 10 Watts and about 2000 Watts, between about 200 Watts andabout 1800 Watts or between about 750 Watts and about 1500 Watts indifferent embodiments. The RF frequency applied in the exemplaryprocessing system may be low RF frequencies less than about 200 kHz,high RF frequencies between about 10 MHz and about 15 MHz or microwavefrequencies greater than or about 1 GHz in different embodiments.Substrate processing region 270 can be maintained at a variety ofpressures during the flow of carrier gases and plasma effluents intosubstrate processing region 270.

In one or more embodiments, the substrate processing chamber 200 can beintegrated into a variety of multi-processing platforms, including theProducer™ GT, Centura™ AP and Endura™ platforms available from AppliedMaterials, Inc. located in Santa Clara, Calif. Such a processingplatform is capable of performing several processing operations withoutbreaking vacuum. Processing chambers that may implement embodiments ofthe present invention may include dielectric etch chambers or a varietyof chemical vapor deposition chambers, among other types of chambers.

Embodiments of the deposition systems may be incorporated into largerfabrication systems for producing integrated circuit chips. FIG. 3 showsone such system 300 of deposition, baking and curing chambers accordingto disclosed embodiments. In the figure, a pair of FOUPs (front openingunified pods) 302 supply substrate substrates (e.g., 300 mm diameterwafers) that are received by robotic arms 304 and placed into a lowpressure holding areas 306 before being placed into one of the waferprocessing chambers 308 a-f. A second robotic arm 310 may be used totransport the substrate wafers from the low pressure holding areas 306to the wafer processing chambers 308 a-f and back. Each wafer processingchamber 308 a-f, can be outfitted to perform a number of substrateprocessing operations including the dry etch processes described hereinin addition to cyclical layer deposition (CLD), atomic layer deposition(ALD), chemical vapor deposition (CVD), physical vapor deposition (PVD),etch, pre-clean, degas, orientation and other substrate processes.

The wafer processing chambers 308 a-f may include one or more systemcomponents for depositing, annealing, curing and/or etching a flowabledielectric film on the substrate wafer. In one configuration, two pairsof the processing chamber (e.g., 308 c-d and 308 e-f) may be used todeposit dielectric material on the substrate, and the third pair ofprocessing chambers (e.g., 308 a-b) may be used to etch the depositeddielectric. In another configuration, all three pairs of chambers (e.g.,308 a-f) may be configured to etch a dielectric film on the substrate.Any one or more of the processes described may be carried out onchamber(s) separated from the fabrication system shown in differentembodiments.

The substrate processing system is controlled by a system controller. Inan exemplary embodiment, the system controller includes a hard diskdrive, a floppy disk drive and a processor. The processor contains asingle-board computer (SBC), analog and digital input/output boards,interface boards and stepper motor controller boards. Various parts ofCVD system conform to the Versa Modular European (VME) standard whichdefines board, card cage, and connector dimensions and types. The VMEstandard also defines the bus structure as having a 16-bit data bus anda 24-bit address bus.

System controller 357 is used to control motors, valves, flowcontrollers, power supplies and other functions required to carry outprocess recipes described herein. A gas handling system 355 may also becontrolled by system controller 357 to introduce gases to one or all ofthe wafer processing chambers 308 a-f. System controller 357 may rely onfeedback from optical sensors to determine and adjust the position ofmovable mechanical assemblies in gas handling system 355 and/or in waferprocessing chambers 308 a-f. Mechanical assemblies may include therobot, throttle valves and susceptors which are moved by motors underthe control of system controller 357.

In an exemplary embodiment, system controller 357 includes a hard diskdrive (memory), USB ports, a floppy disk drive and a processor. Systemcontroller 357 includes analog and digital input/output boards,interface boards and stepper motor controller boards.

Various parts of multi-chamber processing system 300 which containssubstrate processing chamber 200 are controlled by system controller357. The system controller executes system control software in the formof a computer program stored on computer-readable medium such as a harddisk, a floppy disk or a flash memory thumb drive. Other types of memorycan also be used. The computer program includes sets of instructionsthat dictate the timing, mixture of gases, chamber pressure, chambertemperature, RF power levels, susceptor position, and other parametersof a particular process.

A process for etching, depositing or otherwise processing a film on asubstrate or a process for cleaning chamber can be implemented using acomputer program product that is executed by the controller. Thecomputer program code can be written in any conventional computerreadable programming language: for example, 68000 assembly language, C,C++, Pascal, Fortran or others. Suitable program code is entered into asingle file, or multiple files, using a conventional text editor, andstored or embodied in a computer usable medium, such as a memory systemof the computer. If the entered code text is in a high level language,the code is compiled, and the resultant compiler code is then linkedwith an object code of precompiled Microsoft Windows® library routines.To execute the linked, compiled object code the system user invokes theobject code, causing the computer system to load the code in memory. TheCPU then reads and executes the code to perform the tasks identified inthe program.

The interface between a user and the controller may be via atouch-sensitive monitor and may also include a mouse and keyboard. Inone embodiment two monitors are used, one mounted in the clean room wallfor the operators and the other behind the wall for the servicetechnicians. The two monitors may simultaneously display the sameinformation, in which case only one is configured to accept input at atime. To select a particular screen or function, the operator touches adesignated area on the display screen with a finger or the mouse. Thetouched area changes its highlighted color, or a new menu or screen isdisplayed, confirming the operator's selection.

As used herein “substrate” may be a support substrate with or withoutlayers formed thereon. The patterned substrate may be an insulator or asemiconductor of a variety of doping concentrations and profiles andmay, for example, be a semiconductor substrate of the type used in themanufacture of integrated circuits. Exposed “silicon” of the patternedsubstrate is predominantly Si but may include minority concentrations ofother elemental constituents such as nitrogen, oxygen, hydrogen, carbonand the like. Exposed “silicon nitride” of the patterned substrate ispredominantly Si₃N₄ but may include minority concentrations of otherelemental constituents such as oxygen, hydrogen, carbon and the like.Exposed “silicon oxide” of the patterned substrate is predominantly SiO₂but may include minority concentrations of other elemental constituentssuch as nitrogen, hydrogen, carbon and the like. In some embodiments,silicon oxide films etched using the methods disclosed herein consistessentially of silicon and oxygen. The term “precursor” is used to referto any process gas which takes part in a reaction to either removematerial from or deposit material onto a surface. “Plasma effluents”describe gas exiting from the chamber plasma region and entering thesubstrate processing region. Plasma effluents are in an “excited state”wherein at least some of the gas molecules are in vibrationally-excited,dissociated and/or ionized states. A “radical precursor” is used todescribe plasma effluents (a gas in an excited state which is exiting aplasma) which participate in a reaction to either remove material fromor deposit material on a surface. “Radical-fluorine” (or“radical-oxygen”) are radical precursors which contain fluorine (oroxygen) but may contain other elemental constituents. The phrase “inertgas” refers to any gas which does not form chemical bonds when etchingor being incorporated into a film. Exemplary inert gases include noblegases but may include other gases so long as no chemical bonds areformed when (typically) trace amounts are trapped in a film.

The terms “gap” and “trench” are used throughout with no implicationthat the etched geometry has a large horizontal aspect ratio. Viewedfrom above the surface, trenches may appear circular, oval, polygonal,rectangular, or a variety of other shapes. A trench may be in the shapeof a moat around an island of material. The term “via” is used to referto a low aspect ratio trench (as viewed from above) which may or may notbe filled with metal to form a vertical electrical connection. As usedherein, a conformal etch process refers to a generally uniform removalof material on a surface in the same shape as the surface, i.e., thesurface of the etched layer and the pre-etch surface are generallyparallel. A person having ordinary skill in the art will recognize thatthe etched interface likely cannot be 100% conformal and thus the term“generally” allows for acceptable tolerances.

Having disclosed several embodiments, it will be recognized by those ofskill in the art that various modifications, alternative constructions,and equivalents may be used without departing from the spirit of thedisclosed embodiments. Additionally, a number of well known processesand elements have not been described in order to avoid unnecessarilyobscuring the present invention. Accordingly, the above descriptionshould not be taken as limiting the scope of the invention.

Where a range of values is provided, it is understood that eachintervening value, to the tenth of the unit of the lower limit unlessthe context clearly dictates otherwise, between the upper and lowerlimits of that range is also specifically disclosed. Each smaller rangebetween any stated value or intervening value in a stated range and anyother stated or intervening value in that stated range is encompassed.The upper and lower limits of these smaller ranges may independently beincluded or excluded in the range, and each range where either, neitheror both limits are included in the smaller ranges is also encompassedwithin the invention, subject to any specifically excluded limit in thestated range. Where the stated range includes one or both of the limits,ranges excluding either or both of those included limits are alsoincluded.

As used herein and in the appended claims, the singular forms “a”, “an”,and “the” include plural referents unless the context clearly dictatesotherwise. Thus, for example, reference to “a process” includes aplurality of such processes and reference to “the dielectric material”includes reference to one or more dielectric materials and equivalentsthereof known to those skilled in the art, and so forth.

Also, the words “comprise,” “comprising,” “include,” “including,” and“includes” when used in this specification and in the following claimsare intended to specify the presence of stated features, integers,components, or steps, but they do not preclude the presence or additionof one or more other features, integers, components, steps, acts, orgroups.

What is claimed is:
 1. A method of etching a patterned substrate in asubstrate processing chamber, the chamber having a substrate processingregion and a plasma generating region remote from the substrateprocessing region, wherein the patterned substrate has exposed silicon,the method comprising: flowing each of a fluorine-containing precursorand a hydrogen-containing precursor into the remote plasma regionfluidly coupled with the substrate processing region while forming aremote plasma in the remote plasma region to produce plasma effluents,wherein an atomic flow ratio of the precursors is greater than or about25:1 H:F, and wherein the plasma comprises an RF plasma; and etching theexposed silicon by flowing the plasma effluents into the substrateprocessing region through through-holes in a showerhead, wherein atemperature of the patterned substrate during the etching operation isgreater than or about 0° C. and a pressure within the substrateprocessing region is above or about 0.05 Torr and below or about 10Torr.
 2. The method of claim 1 wherein the exposed silicon comprisesexposed polysilicon.
 3. The method of claim 1 wherein the temperature ofthe patterned substrate is greater than or about 20° C. and less than orabout 300° C.
 4. The method of claim 1 wherein the RF plasma power isbetween about 10 Watts and about 15,000 Watts.
 5. The method of claim 1wherein the pressure within the substrate processing region is above orabout 0.1 Torr and below or about 1 Torr.
 6. The method of claim 1wherein forming the remote plasma in the remote plasma region comprisesapplying RF power between about 750 Watts and about 1500 Watts to theplasma region.
 7. The method of claim 1 wherein the remote plasma is acapacitively-coupled plasma.
 8. The method of claim 1 wherein thesubstrate processing region is plasma-free during the operation ofetching the exposed silicon.
 9. The method of claim 1 further comprisinga pre-treatment to remove a native oxide from the exposed silicon beforethe operation of etching the exposed silicon.
 10. The method of claim 9wherein the pre-treatment comprises flowing hydrogen (H₂) into thesubstrate processing region while forming a local pre-treatment plasmaby applying a local plasma power to the substrate processing region. 11.The method of claim 9 wherein the pre-treatment comprises flowing ahydrogen-containing precursor and a fluorine-containing precursor intothe remote plasma region and the resulting plasma effluents into thesubstrate processing region to form solid residue from the native oxideon the exposed silicon, the method further comprising heating thepatterned substrate to sublimate the solid residue.
 12. The method ofclaim 1 further comprising a post-etch treatment after the etchingoperation comprising: flowing at least one of N₂, Ar, He, NO₂, N₂O, H₂,NH₃, O₂ or CH₄ into the substrate processing region while forming alocal plasma by applying a local plasma power above or about 100 Wattsand below or about 3000 Watts.
 13. The method of claim 1 furthercomprising a post-etch treatment after the etching operation, whereinthe post-etch treatment comprises heating the substrate to between 200°C. and about 600° C.
 14. The method of claim 1 wherein the patternedsubstrate further comprises an exposed silicon oxide region and theselectivity of the etching operation (exposed silicon:exposed siliconoxide region) is greater than or about 200:1.
 15. The method of claim 1wherein the patterned substrate further comprises an exposed siliconnitride region and the selectivity of the etching operation (exposedsilicon:exposed silicon nitride region) is greater than or about 200:1.16. The method of claim 1 wherein the patterned substrate furthercomprises an exposed metallic region comprising exposed titanium nitrideor exposed tungsten and the selectivity of the etching operation(exposed silicon:exposed metallic region) is greater than or about100:1.
 17. The method of claim 1 wherein the fluorine-containingprecursor comprises a precursor selected from the group consisting ofhydrogen fluoride, atomic fluorine, diatomic fluorine, nitrogentrifluoride, carbon tetrafluoride and xenon difluoride.
 18. The methodof claim 1 wherein the hydrogen-containing precursor comprises hydrogen(H₂).
 19. The method of claim 1 wherein there are essentially no ionizedspecies or free electrons within the substrate processing region. 20.The method of claim 1 wherein the minimum ID of the through-holes in theshowerhead is between about 0.2 mm and about 5 mm.